Direct current balance adjustment



Sept. 1, 1953 M. MARON 23,707

DIRECT CURRENT BALANCE ADJUSTMENT Original Filed Sept. 25, 1950 32 33BALANCED AMPLIFIER TIME BASE SOURCE I 34 Fig.

Fig. IA

INVENTOR.

MEYER MARON ATTORNEYS Rama sat. 1, 1953 Re. 23,707

UNITED STATES PATENT OFFICE 23,707 DIRECT CURRENT BALANCE ADJUSTMENTMeyer Maren, Passaic, N. J., assignor to Allen B. Du Mont Laboratories,Inc., Clifton, N. J., a corporation of Delaware Original No. 2,631,199,dated March 10, 1953, Serial No. 186,473, September 23, 1950.Application for reissue May 22, 1953, Serial No. 356,924

. (Cl. 179171) Matter enclosed in heavy brackets I: appears in theoriginal patent but forms no part of this 4 Claims.

reissue specification; matter printedin italics indicates the additionsmade by reissue.

. 1 The present invention is concerned with improvements in circuitsparticularly adapted for use in cathode-ray oscillographs.

As is well known, cathode-ray oscillographs Figure 1(A) shows amodification of one portion of the circuit of Figure l.

Referring to Figure 1 of the drawing, the present invention comprises apair of electron tubes form an important tool in the indication of elec-II and I2, illustrated as of the triode type, altrical phenomena bygiving a visual portrayal though it will be understood that the presentof certain electrical characteristics. It is iminvention is not limitedto the use of triodes portant that such oscillographs be adapted forsince other tube types may also be utilized. The use with direct currentor relatively low frecontrol grid l3 of tube II is excited by the inputquency input signals. This requirement necessignals applied to the inputterminals l4 and I5. sitates the use of direct current amplifiers to Asshown, terminal is grounded, while termiincrease the amplitude of inputsignals to,a value nal I4 is connected to grid l3 through a resistorwhich can readily operate the cathode-ray tube 18, shunted by acondenser H. The anode l8 indicator of the oscillograph. The use of suchof tube II is connected directly to a suitable direct current amplifiersintroduces a number source I 9 of positive potential. Source 19 may ofproblems because such amplifiers are inherbe a conventional platevoltage supply. The ently unstable particularly with respect to theircontrol grid 2| of tube I2 is grounded as at 22, zero level condition.It will be understood that and the anode 23 of tube I2 is also connectedto indications on the oscillograph are derived by the positive potentialsource I 9. The cathodes deflection of the cathode-ray beam spot from 24and 25 of respective tubes l I and I2 are cona datum position, usuallydesignated as the zero nected to the fixed terminals of a potentiometerlevel. Hence any random deviation in the zero 28 whose adjustable tap 21is grounded at 28. level will correspondingly create inaccuracies in Acoupling resistor 29 also connects the cathodes the indication. It hastherefore become cus- 5 24 and 25. The balanced output from tubes lltomary to utilize balanced amplifiers which help and l2 is derived fromtheir cathodes 24 and 25, to minimize this zero level instability ofsuch and this output is supplied to a, suitable balanced oscillographs.However, most signals which it amplifier 3| of any desired type ornumber oi may be desired to indicate utilize ground level stages Whoseoutput is then supplied to one set as the datum for potential. Suchsignals are of deflecting plates 32 of a cathode-ray tube. not easilyadapted for use with balanced ampli- In the present instance this isillustrated as the fiers and hence require a form of couplingadaptvertical deflecting plates, although it will be uned tobe excitedby the input signal to produce derstood that the present invention canbe apsuitable balanced output signals to be supplied plied equally wellto the horizontal deflecting to the conventional balanced amplifier. Atthe plates where desired. In the present illustrasame time it isimportant to be able to suitably 35 tion the horizontal deflectingplates 33 are exadjust the zero level or normal beam position of theoscillograph.

The present invention is particularly directed toward improvements insuch coupling circuits which include simplified zero level adjustingmeans. In particular the present invention utilizes a pair of cathodefollower tubes with a special coupling, one of these tubes being excitedby the input signal and both tubes providing a balanced output suitablefor use with subsequent balanced amplifiers.

The objects and advantages of the present invention will become moreapparent from consideration of the following description of a preferredembodiment of the invention, taken in coniunction with the appendeddrawing in which:

Figure 1 is a schematic circuit diagram partly in block form of apreferred form of the invention; and

cited by suitable potentials illustrated as derived from a time basesource 34, which may, for example, be a conventional linear sweepcircuit or a source of sinusoidal voltage or any other desired signal.

In operation, with zero input signal supplied to terminals I4 and I5,tap 21 of potentiometer 2B is adjusted to provide substantially equalpotentials for the two cathodes 24 and 25. This gives a true balancedcondition such that the voltage applied to the plates 32 of thecathoderay tube is the zero level voltage. If any adjustment of the zerolevel position is desired, this can be readily accomplished by theadjustment of tap 21. Upon supplying an input signal to terminals l4 andi5, the cathode current of tube I I will be altered correspondingly,whereby the potential of the cathode 24 will be a facsimile of the inputsignal. At the same time the potential or the cathode 24 is supplied tonal swings.

grounded at 28 as was tap 21 in Figure 1-.

the cathode 25 by the resistor 29. Since grid 2| is grounded at 22, thesignal between cathode 25 andgrid 2| is of opposite polarity from thatbetween cathode 24 and grid ll, This may be most clearly shown from thefollowing illustration. If the signal at terminals I4 and I5 is a directcurrent step signal which makes the control grid I3 more positive, tubeII will draw more current thereby increasing the voltage dropbetweencathode 24 and ground 28, and the potential of cathode 24 will rise andbecome more positive. Resistor 29 correspondingly tends to make cathode25 more positive, which makes grounded grid 2| more negative relative tocathode 25. This in turn reduces the current flow through tube l2 andreduces the potential of cathode 25. Resistor 29 .is made larger inresistance value than potentiometer 25, so that the potential of cathode25 under these circumstances is caused to decrease below zero signalvalue. As a result the input signal increases the potential of cathode24 and decreases the potential of cathode 25, whereby a balanced outputis obtained from cathodes 24, 25 suitable for exciting the subsequentamplifier 3|.

Resistor I6 is a grid-current limiting resistor which serves to protectthe tube II and subsequent tubes from damage due to positive sig-Condenser II preserves the high frequency response of the system.

It will be understood that in place of potentiometer 26 there may beinserted a series connected variable resistor 36 and resistor 37, asshown in Figure 1(A). Their junction 38 is The device of Figure 1(A)will serve to adjust the zero level or balance in the same manner aspotentiometer 26, but does so by increasing or decreasing the currentflow in only one of the two tubes instead of adjusting both tubes as isdone in-Figure 1.

Thus the present invention has provided a simple direct current circuitfor coupling an unbalanced signal to a balanced amplifier, whilepermitting ready adjustment of the balance condition or zero leveladjustment.

Although the invention has been described with respect to a preferredembodiment, it will be understood that variations of the circuit may bemade without departing from the spirit and 4 scope of the inventionwhich is defined in the appended claims.

Whatisclaimed is: 1. A direct current amplifier circuit foroscillographs or the like comprising a pair of electron tubes eachhaving a cathode, a grid and an anode, a source of positive potentialconnected directly to each of said anodes, means for impressing an inputsignal on one of said grids the otherof said grids being grounded, meansproviding a resistance between each of said cathodes and ground, theresistance between at least one of said cathodes and ground beingadjustable to adjust the balance of the outputs from said tubes, aresistor directly connecting said cathodes for transferring signalpotentials I from one of said cathodes to the other independently ofsaid resistance providing means. and a load circuit directly coupled tosaid cathodes to derive a balanced output therefrom.

2. A circuit as in claim 1 wherein said resistance providing meanscomprises a potentiometer having a grounded variable tap.

3. A circuit as in claim 1 wherein said resistance providing meanscomprises two seriesconnected resistors, at least one being variable andtheir Junction being grounded.

4. A circuit as in claim 1 wherein said resistor has greater resistancethan said resistance providing means.

MEYER MARON.

References Cited in the file of this patent or the original patent

